1. Field of the Invention
The present invention relates to a gas diffusion system of electrochemical cells, more particularly to a carbon-based gas diffusion layer with a micro protective layer which prevents the gas diffusion layer from corrosion.
2. Description of the Related Art
Recently, petrochemical products become one of the essential necessaries in daily lives along with the increment of population and the development of the technology. However, people tend to seek for substitute energy with lower contamination due to the shortage of the oil energy, the rising of the price index and the threat of the global warming.
Therefore, fuel cells have received high recognition as a future energy conversion system due to their conversion efficiency and low emission. Fuel cells can directly convert the chemical energy into the electric energy, by electrochemically reacting hydrogen with oxygen to produce electricity and water, which is considered to be friendly to the environment. Furthermore, the water can also be electrolytically decomposed into hydrogen and oxygen gases by means of water electrolysis method. Thus, the combination of a fuel cell and a water electrolysis cell is perfectly referred to as a regenerative fuel cell.
Nevertheless, the conventional fuel cell is apt to encroached while proceeding to water electrolysis. As shown in FIG. 1, a conventional fuel cell 1 mainly consists of end plates 2, 2′, current collectors 3, 3′, flow field plates 4, 4′, gas diffusion layers 5, 5′, catalyst layers 6, 6′, a proton exchange membrane 7 and a circuit unit 8; wherein, the end plates have exits and entrances disposed thereon for gases and water; the gas diffusion layer 5 or 5′ is used for evenly spreading out the gases therein and conducting electrons, usually fabricated by either porous carbon materials (e.g. carbon paper or carbon cloth) or, by metal materials. The carbon-based diffusion layer is light, cheap, and small but tends to react with active oxygen species under the conditions of high temperature or high potential, and is converted into carbon monoxide or carbon dioxide, which results in the corrosion of the diffusion layer; on the other hand, the metallic diffusion layer has better corrosion resistance, but it can still be oxidized to form a low conductive layer on its surface. Besides, it's costly and heavy. In this manner, the carbonic diffusion layer is typically applied to fuel cells and the metallic layer is utilized in water electrolysis cells.
Due to the material issues, the conventional invention requires larger spaces and higher expense to dispose separate devices for the above two energy conversions, for instance of the fuel cell device solely generating electricity and the water electrolysis cell device solely producing hydrogen and oxygen gases, thus still needs improvements.